1. Field of the Invention
The present invention relates to a method and an apparatus for alarming a decrease in tire air-pressure. More particularly, the present invention relates to a method and an apparatus for alarming a decrease in tire air-pressure which are applicable to repair markets and for setting optimal correction factors for the attached tires.
2. Description of Background Art
Apparatuses for detecting a decrease in tire air-pressure through relative comparison of wheel speeds have been conventionally suggested (for instance, in Japanese Examined Patent Publication No. 55322/1993 and others). In such apparatuses, diagonal sums of wheel speeds are compared or judgment is performed only when the vehicle is performing straight-ahead running in which the number of disturbance factors is small for improving accuracy of detection. However, the chances for detecting deflation during only straight-ahead running is remarkably decreased so that it takes a long time to detect deflation. This is especially true when a turning condition is combined with lateral acceleration. In this case, a large lateral acceleration will apply when the vehicle is running at high speed even if the turning movements are made at a large turning radius that is close to straight-ahead driving. Such a situation might result in bursts without any deflation being detected, or when performing running on a mountainous road in which turning movements continue, bead dislodgement will be caused. With the aim of improving such problems, there has been suggested an apparatus in which judgment of deflation is made to be performed also during turning movements and which corrects the judged values with a function introducing therein lateral acceleration and other factors (Japanese Unexamined Patent Publication No. 8713/1994, Japanese Published Patent Publication No. 501040/1996 and Japanese Unexamined Patent Publication No. 164720/1996 and others).
However, since shifts in judged values during turning are corrected in these apparatuses, tuning operations are preliminarily performed for each combination of types of cars/tires for obtaining factors for correction. Conversely, it is necessary to preliminarily obtain factors for turning correction in order to properly make the apparatuses for alarming decrease in air-pressure function. Such apparatuses are thus not appropriate for use in repair markets in which it cannot be foretold to which types of cars the apparatuses are mounted.
It was further necessary for conventional apparatus to set factors capable of preventing large shifts in corrections when the tires are exchanged, for example, from summer tires to winter tires.
The present invention has been made in view of the above facts, and it is an object thereof to provide an apparatus and a method for alarming a decrease in tire air-pressure which are capable of automatically obtaining factors for turning correction and of improving the accuracy of detection of deflation of a tire after fixing a tire to a vehicle.
In accordance a the first aspect of the present invention, there is provided a method for alarming a decrease in tire air-pressure, in which rotational numbers of four tires are detected for judging, on the basis of the detected rotational numbers, whether any of the tire air-pressures is decreased or not, and issuing an alarm in case an internal pressure of a tire is decreased,
wherein in an equation for calculating a judged value for detecting deflation of a tire upon comparing differences of two diagonal sums, correction factor function values including a first factor related to lateral acceleration of the vehicle and a second factor related to lateral acceleration and front and rear wheel ratios are subtracted from actually measured values when performing actual running of the vehicle with the tires being set to specific air-pressures, and the first and second factors are so calculated that a result of subtraction is approximately close to zero and are stored.
In accordance with a second aspect of the present invention, there is provided an apparatus for alarming a decrease in tire air-pressure, in which rotational numbers of four tires are detected for judging, on the basis of the detected rotational numbers, whether any of the tire air-pressures is decreased or not, and issuing an alarm in case an internal pressure of a tire is decreased, the apparatus comprising: a speed detecting means for detecting wheel speeds of the respective tires; a calculating means for calculating and processing a judged value for deflation in which differences between two diagonal sums of rotational numbers of front tires and rotational numbers of rear tires are compared on the basis of the rotational numbers which are obtained from the wheel speeds detected by the speed detecting means; and an optimal factor calculating means in which correction factor function values including a first factor related to lateral acceleration of the vehicle and a second factor related to lateral acceleration and front and rear wheel ratios are calculated by subtracting them from actually measured values when performing actual running of the vehicle with the tires being set to specific air-pressures, and the first and second factors are so calculated that a result of substraction is approximately close to zero and are stored.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.